arch: fix has_transparent_hugepage()

I've just discovered that the useful-sounding has_transparent_hugepage()
is actually an architecture-dependent minefield: on some arches it only
builds if CONFIG_TRANSPARENT_HUGEPAGE=y, on others it's also there when
not, but on some of those (arm and arm64) it then gives the wrong
answer; and on mips alone it's marked __init, which would crash if
called later (but so far it has not been called later).

Straighten this out: make it available to all configs, with a sensible
default in asm-generic/pgtable.h, removing its definitions from those
arches (arc, arm, arm64, sparc, tile) which are served by the default,
adding #define has_transparent_hugepage has_transparent_hugepage to
those (mips, powerpc, s390, x86) which need to override the default at
runtime, and removing the __init from mips (but maybe that kind of code
should be avoided after init: set a static variable the first time it's
called).

Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andres Lagar-Cavilla <andreslc@google.com>
Cc: Yang Shi <yang.shi@linaro.org>
Cc: Ning Qu <quning@gmail.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Vineet Gupta <vgupta@synopsys.com>		[arch/arc]
Acked-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>	[arch/s390]
Acked-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/arc/include/asm/hugepage.h

@@ -61,8 +61,6 @@ static inline void set_pmd_at(struct mm_struct *mm, unsigned long addr,
 extern void update_mmu_cache_pmd(struct vm_area_struct *vma, unsigned long addr,
 				 pmd_t *pmd);
 
-#define has_transparent_hugepage() 1
-
 /* Generic variants assume pgtable_t is struct page *, hence need for these */
 #define __HAVE_ARCH_PGTABLE_DEPOSIT
 extern void pgtable_trans_huge_deposit(struct mm_struct *mm, pmd_t *pmdp,

arch/arm/include/asm/pgtable-3level.h

@@ -281,11 +281,6 @@ static inline void set_pmd_at(struct mm_struct *mm, unsigned long addr,
 	flush_pmd_entry(pmdp);
 }
 
-static inline int has_transparent_hugepage(void)
-{
-	return 1;
-}
-
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_PGTABLE_3LEVEL_H */

arch/arm64/include/asm/pgtable.h

@@ -314,11 +314,6 @@ static inline int pmd_protnone(pmd_t pmd)
 
 #define set_pmd_at(mm, addr, pmdp, pmd)	set_pte_at(mm, addr, (pte_t *)pmdp, pmd_pte(pmd))
 
-static inline int has_transparent_hugepage(void)
-{
-	return 1;
-}
-
 #define __pgprot_modify(prot,mask,bits) \
 	__pgprot((pgprot_val(prot) & ~(mask)) | (bits))
 

arch/mips/include/asm/pgtable.h

@@ -468,6 +468,7 @@ static inline int io_remap_pfn_range(struct vm_area_struct *vma,
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 
+#define has_transparent_hugepage has_transparent_hugepage
 extern int has_transparent_hugepage(void);
 
 static inline int pmd_trans_huge(pmd_t pmd)

arch/mips/mm/tlb-r4k.c

@@ -400,19 +400,20 @@ void add_wired_entry(unsigned long entrylo0, unsigned long entrylo1,
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 
-int __init has_transparent_hugepage(void)
+int has_transparent_hugepage(void)
 {
-	unsigned int mask;
-	unsigned long flags;
-
-	local_irq_save(flags);
-	write_c0_pagemask(PM_HUGE_MASK);
-	back_to_back_c0_hazard();
-	mask = read_c0_pagemask();
-	write_c0_pagemask(PM_DEFAULT_MASK);
+	static unsigned int mask = -1;
 
-	local_irq_restore(flags);
+	if (mask == -1) {	/* first call comes during __init */
+		unsigned long flags;
 
+		local_irq_save(flags);
+		write_c0_pagemask(PM_HUGE_MASK);
+		back_to_back_c0_hazard();
+		mask = read_c0_pagemask();
+		write_c0_pagemask(PM_DEFAULT_MASK);
+		local_irq_restore(flags);
+	}
 	return mask == PM_HUGE_MASK;
 }
 

arch/powerpc/include/asm/book3s/64/pgtable.h

@@ -219,6 +219,7 @@ extern void set_pmd_at(struct mm_struct *mm, unsigned long addr,
 		       pmd_t *pmdp, pmd_t pmd);
 extern void update_mmu_cache_pmd(struct vm_area_struct *vma, unsigned long addr,
 				 pmd_t *pmd);
+#define has_transparent_hugepage has_transparent_hugepage
 extern int has_transparent_hugepage(void);
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 

arch/powerpc/include/asm/pgtable.h

@@ -65,7 +65,6 @@ extern int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
 		       struct page **pages, int *nr);
 #ifndef CONFIG_TRANSPARENT_HUGEPAGE
 #define pmd_large(pmd)		0
-#define has_transparent_hugepage() 0
 #endif
 pte_t *__find_linux_pte_or_hugepte(pgd_t *pgdir, unsigned long ea,
 				   bool *is_thp, unsigned *shift);

arch/s390/include/asm/pgtable.h

@@ -1223,6 +1223,7 @@ static inline int pmd_trans_huge(pmd_t pmd)
 	return pmd_val(pmd) & _SEGMENT_ENTRY_LARGE;
 }
 
+#define has_transparent_hugepage has_transparent_hugepage
 static inline int has_transparent_hugepage(void)
 {
 	return MACHINE_HAS_HPAGE ? 1 : 0;

arch/sparc/include/asm/pgtable_64.h

@@ -681,8 +681,6 @@ static inline unsigned long pmd_trans_huge(pmd_t pmd)
 	return pte_val(pte) & _PAGE_PMD_HUGE;
 }
 
-#define has_transparent_hugepage() 1
-
 static inline pmd_t pmd_mkold(pmd_t pmd)
 {
 	pte_t pte = __pte(pmd_val(pmd));

arch/tile/include/asm/pgtable.h

@@ -487,7 +487,6 @@ static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
 }
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-#define has_transparent_hugepage() 1
 #define pmd_trans_huge pmd_huge_page
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 

arch/x86/include/asm/pgtable.h

@@ -181,6 +181,7 @@ static inline int pmd_trans_huge(pmd_t pmd)
 	return (pmd_val(pmd) & (_PAGE_PSE|_PAGE_DEVMAP)) == _PAGE_PSE;
 }
 
+#define has_transparent_hugepage has_transparent_hugepage
 static inline int has_transparent_hugepage(void)
 {
 	return boot_cpu_has(X86_FEATURE_PSE);

include/asm-generic/pgtable.h

@@ -806,4 +806,12 @@ static inline int pmd_clear_huge(pmd_t *pmd)
 #define io_remap_pfn_range remap_pfn_range
 #endif
 
+#ifndef has_transparent_hugepage
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+#define has_transparent_hugepage() 1
+#else
+#define has_transparent_hugepage() 0
+#endif
+#endif
+
 #endif /* _ASM_GENERIC_PGTABLE_H */